Silicon is an extremely attractive material platform for integrated optics at telecommunications wavelengths, particularly for integration with CMOS circuits. Low loss waveguides, high-Q resonators, high speed modulators, efficient couplers, and optically pumped lasers have been shown. Developing detectors and electrically pumped lasers at telecom wavelengths are the two main technological hurdles before silicon can become a comprehensive platform for integrated optics.
Silicon's bandgap of 1.12 eV makes it challenging to build a silicon-based detector in this near infrared. Silicon has minimal absorption of photons in this regime, at least in the bulk, defect-free case. Two-photon absorption can potentially be used to circumvent this limit and build a detector, but for practical power levels efficiency is poor. Approaches to detection have typically relied upon bonded III-V materials, on integrating Germanium or SiGe, or more recently, through volume defect creation via ion implantation.
A photocurrent has also been observed in undamaged silicon waveguides, and has been possibly attributed to an effect from the surface of the waveguide, though quantum efficiencies of only 0.24% were shown.